Metal treating process employing a heat-resistant lubricant composed of alkali metalborate and alkali metal phosphate



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METAL TREATING PROCESS EMPLOYING A HEAT-RESISTANT LUBRICANT COMPOSED 0F ALKALI METAL BORATE AND ALKALI METAL PHOSPHATE Filed May 14, 1957 DIAGRAM ALKAQ-l METAL PHOSPHATE m m, w w R i z T m w 1.? M w M Tu w m 1N 2 1, M H L nw .aw o w A B a .0500

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All o I mgizumtu IN VE N TOPS U #CJM United States Patent 2,990,610 METAL TREATING PROCESS EMPLOYING A HEAT-RESISTANT LUBRICANT COMPOSED 0F ALKALI METAL BORATE AND ALKALI V METAL PHOSPHATE Werner Liickerath and Georg Graue, Hamburg, Lower Rhine, Germany, assignors to Phoenix-Rheinrohr Aktiengesellschaft Vereinigte Huttenund Rohrenwerke Filed May 14, 1957, 'Ser. No. 659,113 4 Claims priority, application Germany May 16,, 1956 13 Claims. (Cl. 29-528) In the deformation of metals by heat, for example when rolling, drawing or pressing metals, the frictional resistance between the work and the deforming tools must be reduced as much as possible on the one hand in order to keep the wear on the tool and the power required, within economical limits, and on the other hand to obtain a good surface on the work. It has been found by experience that a smooth surface can only be obtained if the work is freed before its deformation from the scale resulting from the thermal pre-treatment. The removal of the scale can be effected either by mechanical means or by the use of pickling baths, for example by treatment with aqueous solutions of acids. Also salt baths consisting of sodium hydroxide, sodium hydride or of metallic sodium, as well as solid descaling agents consisting of mixtures of sodium sulphate and phosphoric acid, have previously been used for this purpose. Another prior proposal was to remove the scale by the application of a molten glaze which, on cooling, causes the scale to break away from the surface of the work. For this purpose, mixtures of waterglass and soda with borax and phosphate have been proposed.

It is also known to apply a lubricant to the work which has been descaled in one way or another before its deformation by heat, in which case it was found that it is particularly advantageous to phosphoratise the surface of the work before the application of the lubricant in order to obtain a good adherence.

All these measures which have been employed for the preparation of the work for heat deformation processes are complicated and require a great expenditure of time and working means. The object of the present invention, therefore, is to provide an agent which considerably facilitates the pre-treatment of work which is to be deformed by heat and which is also better in the effects produced than the agents previously used for this purpose. An idea lubricant should preferably comply with the following requirements. It should not decompose under the high stresses caused by the heat and pressure to which it is subjected during the working process; it should possess as far as possible a uniform low viscositythroughout a wide range of temperature and a good wetting capacity. It must also form on the surface of the work -a coherent film which adheres well to the work and must also be capable of being removed again from the surface of the treated work with as littel expense as possible and, for this reason, should preferably be water-soluble. A lubricant which meets 'all these requirements has not previously been found. Y i

Organic substances such as, for example, oils and calcium 'soaps which have previously been proposed for this purpose do not stand up to the usual working temperatures of 800-l000 C. because they decompose and evaporate at such temperatures. Also the inorganic substances which have been proposed for lubricating purposes such as metal suspensions or colloidal thorium hydroxide, which have been proposed for drawing tungsten wire, and vanadium hydroxide or aluminium powder and more recently molybdenum sulphide for iron, are subject to undesirable alterations during the working process, because they are all transformed into their oxides at the abovementioned working temperatures and then no longer act as lubricants, but act on the contrary as grinding agents, with the consequence that the power requirements are increased and there is increased wear on the tools. Also,

complex inorganic substances which are highly viscous, at the said deformation temperatures, for example incompletely dehydrated polyphosphoric acid or polyboric acid have previously been proposed. Finally, experiments I have also been made with silicate glasses or glazes which partly or completely melt at high temperatures and thereby form a viscous mass. These agents, however, are disadvantageous because they are very difiicult to remove later'from the work.

It has, therefore, not yet been possible to provide a lubricating agent which can be considered to be idea in the sense of the present invention. The invention, therefore, has for its object to find a lubricant for use in the heat deformation of metallic work pieces having the aforesaid desirable properties. According to the invention, it consists of a mixture of an alkali metal borate, for example sodium borate, preferably sodium tetraborate (borax) and an alkali metal phosphate, for example potassium phosphate. The composition of the mixture is preferably such that it contains 5-20 parts of potassium phosphate to one part of sodium tetraborate.

The drawing shows a fusion diagram of various mixtures composed in accordance with the invention. The drawing presents melting point graphs of various mixtures of alkali metal phosphates and alkali metal tetraborates, Viz, KPO3'K2B407; NaPO3-Na2B4o7; NaPO3 K2B407; and KPO Na B O The low melting eutectic compositions are thus evident. It will be seen from the diagram that a lubricant composed of one part of borax and 9 parts of potassium phosphate (KPO has the lowest melting temperature. It is, therefore, particularly suitable for many purposes.

It is indeed known that molten sodium tetraborate (borax) is able to dissolve metal oxides, but its melting point, which is about 740 C., is so high that, for this reason, it cannot be used by itself as a lubricant. Further, it does not form a uniform adherent surface film.

Comprehensive experiments which have been carried out by the inventor were the first to show that in mixture with potassium phosphate a small proportion of borax is suflicient to obtain an excellent scale-loosening effect and that certain mixtures of substances in accordance with the invention have moreover a softening range which already begins at 300 C. The low softening point on the one hand and the very great resistance to temperature of the mixtures on the other hand ensure the formation of a satisfactory film of lubricant at temperatures up to 1,000" C. and more, and, therefore, make the mixture pro-eminently suitable as a lubricant for articlm which have to be deformed or worked when heated. The stability of the film of lubricant is probably due to the fact that the lubricant t 3 causes phosphatising of the surface of the work which is known to be particularly advantageous for uniform adherence of lubricants.

A strong corrosion retarding effect is associated with the phosphatising. Experiments have shown that, for example, metal sheets which were treated with the lubricant subject of the invention have much greater resistance to corroding influences than similar untreated sheets.

The removal of the scale from the work and the formation of the desired smooth surface on it with the aid of the lubricant of the invention, can take place in a bath which precedes the deforming apparatus. It is, however, also possible to apply the mixture in powdery condition to the work immediately before its deformation. It is particularly advantageous to use the mixture in the form of an aqueous solution, in which case the solvent evaporates at the high temperature and thereby exerts at the same time a cooling effect on the deforming tools.

Of course, the lubricant of the invention is not limited to use in the deformation of metals. It can be used in all cases in which lubricated parts are exposed to the action of high temperatures, for example in furnaces through which the work travels, furnace doors and the like.

We claim:

1. In the process of physical deformation of a metal object under the application of heat, in which the metal is subjected to deforming stress at elevated temperatures, the improvement comprising de-scaling, lubricating, and phosphatizing the surface of said object by coating said surface, prior to said deformation, with a lubricant material which does not decompose and does not evaporate at the deformation temperature and which is readily removable from the object subsequently to said deformation, said lubricant material consisting essentially of a water-soluble eutectic mixture of a molecularly dehydrated alkali metal phosphate and an alkali metal tetraborate, the alkali metal being taken from the group consisting of potassium and sodium, which eutectic begins to soften at a temperature not higher than said working temperature and below the melting temperatures of the phosphate and borate.

2. The process defined in claim 1, the material being applied to the surface in aqueous solution.

3. In the process of physical deformation of a ferrous metal object under the application of heat, at Working temperatures of at least about 800 C., the improvement comprising, prior to said deformation, de-scaling, lubricating, and phosphatizing the surface of said object by coating said surface with an organic substance-free, lubricant material which does not decompose and does not evaporate at said working temperature and which is readily removable from the object subsequently to said deformation, said material consisting essentially of a water-soluble eutectic mixture of KPO and sodium tetraborate, which eutectic begins to soften at about 300 C.

4. In the process of physical deformation of a metal object under the application of heat, in which the metal is subjected to deforming stress at elevated temperatures the improvement comprising, prior to said deformation, de-scaling, lubricating, and phosphatizing the surface of said object by coating said surface with a lubricant material which does not decompose and does not evaporate at said working temperature and which is readily removable from the object subsequently to said deformation, said material consisting essentially a water-soluble eutectic mixture of a molecularly dehydrated alkali metal phosphate and an alkali metal tetraborate, the alkali metal beingtaken from the group consisting of potassiumv and sodium, which eutectic begins to soften at a temperature below said working temperature, said material being free of heatdecomposable organic substance.

5. In the process of-lubricatingthe surface of a metal object which is subject to an elevated temperature the improvement comprising coating said surface with a material which does not decompose and does not evaporate at said temperature and which is readily removable from the object subsequently, said material consisting essentially of a water-soluble eutectic mixture of a molecularly dehydrated alkali metal phosphate and an alkali metal tetraborate, the alkali metal being taken from the group consisting of potassium and sodium, which eutectic begins to soften at a temperature below the temperature to which the object is subjected.

6. The process defined in claim 5, the material being applied to the surface in aqueous solution.

7. In the process of lubricating the surface of a metal object which is subject to temperatures of at least about 800 C., the improvement comprising coating said surface with a material which does not decompose and does not evaporate at said temperature and which is readily removable from the object subsequently, said material consisting essentially of a water-soluble eutectic mixture of sodium tetraborate and KPO 8. In the process of lubricating a hot ferrous metal surface, the improvement comprising forming thereon a coating of a lubricant consisting essentially of a molten mixture of 1 part of an alkali metal tetraborate and 5 to 20 parts of a molecularly dehydrated alkali metal phosphate, the alkali metal being taken from the group consisting of potassium and sodium, said molten mixture being substantially free of heat-decomposable organic matter.

9. In the process of physical deformation of a ferrous metal object under the application of heat, in which the metal is subjected to deforming stress at working temperatures of at least about 800 C., the improvement comprising de-scaling, lubricating, and phosphatizing the surface of said object by coating the surface of said object, prior to said deformation, with a lubricant material which does not decompose and does not evaporate at the deformation temperature and which is readily removable from the object subsequently to said deformation, said lubricant material consisting essentially of a water-soluble eutectic mixture of potassium phosphate, namely KPO and an alkali metal tetraborate taken from the group consisting of potassium and sodium tetraborate, which eutectic begins to soften at a temperature not higher than said working temperature and below the melting temperature of the phosphate and borate.

10. In. the process of physical deformation of a ferrous metal object under the application of heat, in which the metal is subjected to deforming stress at working temperatures of at least about 800 C., the improvement comprising de-scaling, lubricating, and phosphatizing the surface of said object by coating the surface of said object, prior to said deformation, with a lubricant material which does not decompose and does not evaporate at the deformation temperature and which is readily removable from the object subsequently to said deformation, said lubricant material consisting essentially of a water-soluble eutectic mixture of sodium phosphate, namely NaPO and an alkali metal tetraborate taken from the group consisting of potassium and sodium tetraborate, which eutectic begins to soften at a temperature not higher than said working temperature and below the melting temperature of the phosphate and borate.

11. A process for phosphatizing a metal surface comprising contacting the surface with a molten eutectic mixture of a molecularly dehydrated alkali metal tetraborate and an alkali metal phosphate, the alkali metal being taken from the group consisting of potassium and sodium.

12. A process of phosphatizing the surface of ferrous metal comprising coating said surface with a molten eutectic mixture of a molecularly dehydrated alkali metal tetraborate and alkali metal phosphate, the alkali metal being taken from the-group consisting of potassium and sodiunu.

'13. A process of phosphatizing the surface of ferrous 2,538,917 metal comprising maintaining said surface in contact 2,618,530 with a molten material consisting essentially of a eutectic 2,709,516 mixture of KPO and sodium tetraborate. 2,753,304

5 References Cited in the file of this patent UNITED STATES PATENTS 668,032

Re.23,-184 Whitbeck Dec. 20, 1949 2,291,958 Garrison Aug. 4, 1942 ,469,473 Orozco et a1. May 10, 1949 2,530,837 Orozco Nov. 21, 1950 6 Sejournet et a1. Ian. 23, 1951 Gardner Nov. 18, 1952 Trembicki May 31, 1955 Orozco July 3, 1956 FOREIGN PATENTS Germany Nov. 24, 1938 OTHER REFERENCES 10 Bastian: Metal Working Lubricants, McGraw-Hill Book Co. (1951), page 19.

Chem. Abstracts, vol. 31, page 1288 

1. IN THE PROCESS OF PHYSICAL DEFORMATION OF A METAL OBJECT UNDER THE APPLICATION OF HEAT, IN WHICH THE METAL IS SUBJECTED TO DEFORMING STRESS AT ELEVATED TEMPERATURES THE IMPROVEMENT COMPRISING DE-SCALING, LUBRICATING, AND PHOSPHATIZING THE SURFACE OF SAID OBJECT BY COATING SAID SURFACE, PRIOR TO SAID DEFORMATION, WITH A LUBRICANT MATERIAL WHICH DOES NOT DECOMPOSE AND DOES NOT EVAPORATE AT THE DEFORMATION TEMPERATURE AND WHICH IS READILY REMOVABLE FROM THE OBJECT SUBSEQUENTLY TO SAID DEFORMATION, SAID LUBRICANT MATERIAL CONSISTING ESSENTIALLY OF A WATER-SOLUBLE EUTECTIC MIXTURE OF A MOLECULARLY DEHYDRATED ALKALI METAL PHOSPHATE AND AN ALKALI METAL TETRABORATE, THE ALKALI METAL BEING TAKEN FROM THE GROUP CONSISTING OF POTASSIUM AND SODIUM, WHICH EUTECTIC BEGINS TO SOFTEN AT A TEMPERATURE NOT HIGHER THAN SAID WORKING TEMPERATURE AND BELOW THE MELTING TEMPERATURES OF THE PHOSPHATE AND BORATE. 